Pressure sensitive adhesive sheet a pressure sensitive label and a laminate utilizing a specified pressure sensitive adhesive layer

ABSTRACT

A pressure sensitive adhesive sheet or label comprising an adhesive coated substrate of paper or synthetic resin film, the adhesive coating containing an acrylic copolymer prepared by copolymerization of 0.1 to 20 weight % of (A) at least one unsaturated monomer of the formula: ##STR1## wherein R is hydrogen or methyl group, R 1  and R 2  are hydrogen or a C 1  -C 4  alkyl, n is 1 to 4; 0.01 to 10 weight % or (B) at least one unsaturated monomer of the formula: ##STR2## wherein Y is an organic group having a radical polymerizable unsaturated bond and R 3 , R 4  and R 5  are an aryl, or an unsubstituted or substituted alkyl; 0 to 10 weight % of (C) at least one unsaturated monomer of the formula: ##STR3## wherein R 6  R 7 , R 8 , R 9  and R 10  are hydrogen or --CH 2  OH; 60 to 99.89 weight % of (D) at least one unsaturated monomer of the formula: ##STR4## wherein R 11  is hydrogen or methyl group and R 12  is a C 1  -C 14  alkyl. 
     A laminate can be prepared by laminating sheets or plastic molded articles with an adhesive coating composition as set forth above.

This is a division of application Ser. No. 07/800,533 filed Nov. 27,1991, now U.S. Pat. No. 5,278,271, issued Jan. 11, 1994.

BACKGROUND OF THE INVENTION

1Field of the Invention

The present invention relates to a novel pressure sensitive adhesivecomposition which has excellent blister resistance, excellentremovability and no corrosive property against substrate and novelpressure sensitive adhesive sheet, label and laminate utilizing theadhesive composition and useful for attaching the sheet, the label andthe laminate to molded articles. More particularly, the presentinvention relates to a novel pressure sensitive adhesive compositionwhich has excellent cohesive strength and heat resistance and isfavorably utilized for surface protecting sheets having resistanceagainst formation of blisters, such as bubbles and lifting, onapplication to the surface of a substrate and good removability withoutleaving dirty remainings and for polyester tape electric insulatorshaving no corrosive property against metals, such as copper wires, andalso relates to novel pressure sensitive adhesive sheet, label andlaminate having excellent resistance against formation of blisters byutilizing the adhesive composition.

2. Description of the Prior Art

As is well known, pressure sensitive adhesive sheets having a coatinglayer of a pressure sensitive adhesive are widely used. This is becausethe pressure sensitive adhesive sheets can be readily bonded to thesurface of various substrates conveniently by merely putting on andlightly pressing to the substrate surface and, different from adhesivesin general, the pressure sensitive adhesive forming the coating layer ofthe sheet contains no organic solvent so that no problem ofenvironmental pollution are caused thereby.

As a consequence of the trend in recent years that light weight articlesare preferred, the quantity of plastic products is rapidly increasingyear by year. Thus, the occasion in which pressure sensitive adhesivesheets are attached to plastic goods or plastic packages of goods as alabel is also increasing rapidly. Pressure sensitive adhesive sheets arequite often applied to the surface of polycarbonate resin plates for thepurpose of protection of the surface from scratching and adjustment ofsun light transmission.

Pressure sensitive adhesive sheets in general have a serious problemthat, when a pressure sensitive adhesive sheet is applied and bonded tothe surface of an article made of acrylic resin, polycarbonate resin andthe like, so-called blisters are not rarely formed due to incompletesqueeze out of the gas between the substrate surface and the pressuresensitive adhesive sheet attached as a label or a protecting sheet. Thisproblem has been unavoidable when the face stock film of the pressuresensitive adhesive sheet is made of a resin having gas barrier propertysuch as conventional polyester resins. This problem is particularlyserious at high temperatures or in conditions of high temperature andhigh humidity.

When blisters are caused in the pressure sensitive adhesive sheetattached to the surface of an article as a label, not only the articlehas a very unsightly appearance to decrease the commercial value butalso the label and the like attached to the surface are liable toeventual falling. In a printed label made of a see-through pressuresensitive adhesive sheet, in particular, it is unavoidable that theappearance is extremely poor because the layer of the adhesive coatingexhibits a pockmarked or white and cloudy appearance through theface-stock film.

Surface protecting sheets made from pressure sensitive adhesivematerials coated on the surface of paper or synthetic resin films arewidely utilized for metal plates, such as stainless steel plate,aluminum plate, steel plates and the like, glass products, molded resinproducts, such as ABS resin plates, acrylic resin plates and styreneresin plates, and the like other various products for the purpose ofpreventing corrosion and staining of the surface.

Pressure sensitive adhesive sheets prepared by coating a pressuresensitive adhesive material comprising as the main component thereofnatural rubber or synthetic rubber compounded with resinous materials onthe surface of a substrate, such as paper and synthetic resin film, havebeen widely used for the surface protecting sheets. In the pressuresensitive adhesive material used for these pressure sensitive adhesivesheets, though the low initial adhesive strength required for attaininggood removability can be provided, adhesive strength is increased duringstorage time remarkably. The increase of the adhesive strength causes aproblem that removal of the pressure sensitive adhesive sheet from thesurface of the substrate becomes very difficult and, moreover, a part ofthe adhesive material very often remains on the surface of the substratebecause of inferior stability of the pressure sensitive adhesivematerial against weathering.

Recently, acrylic pressure sensitive adhesive materials are widely usedfor the surface protecting sheets because of the good resistance againstweathering. When the acrylic pressure sensitive adhesive material isutilized for the surface protecting sheets, the adhesive material isrequired to have high internal cohesive strength so that it has goodremovability and does not have adhesive transfer to the surface of thesubstrate. By this reason, acrylic polymers utilized in the adhesivematerial for the surface protecting sheets are modified bycopolymerization with a monomer having carboxyl group as a functionalgroup and the copolymer prepared are compound with a polyisocyanatecompound, melamine resin, metal salts and the like as the externalcrosslinking agent and then crosslinked.

However, the acrylic pressure sensitive adhesive material has a problemthat the adhesive material must be aged by standing for a long time atthe room temperature or by heating because the adhesive material has lowrate of crosslinking and the initial adhesive strength can not be keptat a low value immediately after the application to the substrate. Theacrylic pressure sensitive adhesive material has another problem thatadhesive strength is inevitably increased during storage time becausethe adhesive material contains copolymer comprising a monomer having acarboxyl group and removability from the substrate is poor.

In some cases, surface active agents, silicones, plasticizers orinorganic salts are added to the pressure sensitive adhesive materialfor the purpose of preventing the increase of the adhesive strength.However, this method has a problem that deficient printing anddelamination sometimes occur because of contamination of the surface ofsubstrate by bleeding of the added ingredients.

For the purpose of increasing rate of crosslinking and improvingefficiency of processing, density of crosslinking in the pressuresensitive adhesive material is increased and cohesive strength isenhanced by using a copolymer comprising two or more kinds of monomerhaving functional groups, such as carboxyl group, methylol group,glycidyl group and the like, followed by crosslinking with an externalcrosslinking agent, such as polyisocyanate compounds, melamine resins,metal salts and the like. However, this type of pressure sensitiveadhesive material is lacking in anchoring power to paper or syntheticfilm to cause problems such as transfer of the adhesive material to thesubstrate and removal or delamination during application to thesubstrate because of low adhesive strength caused by too high cohesivestrength.

As exemplified above, conventional pressure sensitive adhesive sheetsfor surface protection do not satisfy the requirement that thenon-staining property to the substrate and the balancedadhesive-removable properties are simultaneously attained.

Excellent adhesive strength, creep property and solvent resistance arerequired for polyester tapes for electric insulation as good industrialmaterials. Electric and electronic apparatus have been making progressin the direction of decreased size, light weight and higher performancein recent years and, along with this progress, tapes having excellentcorrosion resistance, particularly resistance against electro-corrosionand resistance against coloring of copper, are being required moreurgently. Acrylic pressure sensitive adhesive materials using comonomershaving carboxyl group or hydroxyl group in a lowest possible mount havebeen mainly utilized for polyester tapes for electric insulation toachieve better balance between adhesive strength, creep properties andweatherability. However, pressure sensitive adhesive tapes havingsufficiently excellent corrosion resistance have not been successfullyprepared.

SUMMARY OF THE INVENTION

The present invention accordingly has an object to provide a pressuresensitive adhesive composition having excellent characteristics such (1)that the adhesive composition can provide an adhesive sheet which canprevent formation of blisters causing lifting and bubbling of the sheetwhen the sheet is applied to plastic molded plates, particularly topolycarbonate plates; (2) that the adhesive composition can provide asurface protecting sheet which has suitable initial adhesive strength,low rate of increase of the adhesive strength and excellent removabilitywithout leaving stain on the substrate; and (3) that the adhesivecomposition can provide a tape or a sheet for electric insulation havingexcellent creep properties, solvent resistance and corrosion resistancein addition to the favorable properties described above. Further objectsof the invention is to provide sheets, labels and laminates having theabove favorable properties by utilizing said pressure sensitive adhesivecomposition.

The present invention has been completed as a result of the extensiveinvestigations undertaken with an object of providing a pressuresensitive adhesive composition having the favorable properties describedabove, leading to a discovery that the acrylic copolymers comprisingmonomer units having a carboxyl group utilized in conventional pressuresensitive adhesive compositions as the main composition thereof for thepurpose of providing increased cohesive strength, heat resistance andadhesive strength have problems caused by the monomer units having acarboxyl group (1) that blisters are formed by insufficient adhesivestrength in a condition of high temperature and high humidity and bylack of wetting of the adhesive composition on the surface of thesubstrate, (2) that removabillty becomes poor by increase of adhesivestrength and (3) that corrosion readily occurs and that the objectdescribed above can be achieved by a composition comprising as the maincomponent thereof an acrylic copolymer utilizing a comonomer unit havinga specific functional group without utilizing a comonomer having acarboxyl group.

Thus, the present invention provides a pressure sensitive adhesivecomposition comprising as the main component thereof an acryliccopolymer prepared by copolymerization of from 0.1 to 20 weight % of thecomponent (A) comprising at least one unsaturated monomer selected formthe group consisting of the unsaturated monomers having the structure ofthe general formula: ##STR5## wherein R is a hydrogen atom or methylgroup, R¹ and R² are a hydrogen atom or an alkyl group of 1 to 4 carbonatoms, respectively, n is an integer from 1 to 4 and R¹ and R² may thesame or different;

from 0.01 to 10 weight % of the component (B) comprising at least oneunsaturated monomer selected form the group consisting of theunsaturated monomers having the structure of the general formula:##STR6## wherein Y is an organic group having a radical polymerizableunsaturated bond and R³, R⁴ and R5 are an aryl, alkyl or substitutedalkyl group, respectively, and may be the same or different with eachother;

from 0 to 10 weight % of the component (C) comprising at least oneunsaturated monomer selected form the group consisting of theunsaturated monomers having the structure of the general formula:##STR7## wherein R⁶, R⁷, R⁸, R⁹ and R¹⁰ are a hydrogen atom or --CH₂ OHgroup, respectively, and may be the same or different with each other;and

from 60 to 99.89 weight % of the component (D) comprising at least oneunsaturated monomer selected form the group consisting of theunsaturated monomers having the structure of the general formula:##STR8## wherein R¹¹ is a hydrogen atom or methyl group and R¹² is analkyl group of I to 14 carbon atoms.

The present invention also provides an adhesive sheet which is preparedby coating the pressure sensitive adhesive composition described aboveon a substrate.

The present invention also provides a label which is prepared by coatingthe pressure sensitive adhesive composition described above on asubstrate.

The present invention also provides a laminate which is prepared bylaminating sheets or plastic molded articles through an adhesive layerof the pressure sensitive adhesive composition described above.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described in more detail in the following.

The pressure sensitive adhesive composition of the invention isdescribed first.

The component (A) which is a functional monomer utilized in theinvention is an unsaturated monomer having the structure of the generalformula [1]: ##STR9## wherein R is a hydrogen atom or methyl group, R¹and R² are a hydrogen atom or an alkyl group of 1 to 4 carbon atoms,preferably from 1 to 2 carbon atoms, respectively, n is an integer from1 to 4, preferably from 2 to 3, and R¹ and R² may the same or different.

Examples of the component (A) are: N,N-dimethylaminoethylacrylamide,N,N-diethylaminoethylacrylamide, N-methylaminoethylacrylamide,aminoethylacrylamide, N-ethylaminoethylacrylamide,N,N-dibutylaminoethylacrylamide, N,N-dimethylaminopropylacrylamide,N,N-diethylaminopropylacrylamide and methacrylamides corresponding tothe above acrylamide compounds in which a methyl group is substituted atthe α-carbon of the acryamides. Preferable examples of the component (A)are N,N-dimethylaminoethylacrylamide, N,N-dimethylaminopropylacrylamide,N,N-diethylaminoethylacrylamide, N,N-diethylaminopropylacrylamide,N,N-dimethyiaminoethylmethacrylamide,N,N-dimethylaminopropylmethacrylamide,N,N-diethylaminoethylmethacrylamide andN,N-diethylaminopropylmethacrylamide.

The unsaturated monomer of the component (A) may be utilized singly oras the combination of two or more kinds thereof in the component (A).

The component (A) exhibits catalytic effect when the acrylic copolymeris crosslinked by using crosslinking agents which will be describedlater. The component (A) also provides the acrylic copolymer of theinvention with excellent elongation which conventional acryliccopolymers comprising monomer units having carboxyl group, monomer unitshaving hydroxyl group or monomer units having epoxy group can not haveand, at the same time, with the effect of prevention of decrease ofadhesive strength in the condition of high temperature and highhumidity. Thus, the component (A) is effective for providing a polymerhaving excellent resistance against blister formation.

The content of the component (A) is generally in the range from 0.1 to20 weight %. When the content of the component (A) is less than 0.1weight %, the favorable effect of the composition is not sufficientlyexhibited and, when the content is more than 20 weight %, problems occurthat the adhesive strength is decreased so much that the composition isnot suitable for use as the blister resistant adhesive composition andthat the composition tends to corrode metals because of excessivestrength of alkaline property.

The preferable content of the component (A) is different according tothe application to which the pressure sensitive adhesive of theinvention is utilized. When it is utilized as the blister resistantpressure sensitive adhesive, the content of the component (A) ispreferably in the range from 2.5 to 15 weight %, more preferably in therange from 2.5 to 10 weight %. When it is utilized as the P.S.A. of thesurface protection, the content of the component (A) is preferably inthe range from 1 to 10 weight %, more preferably in the range from 1 to5 weight %. When it is utilized as the P.S.A. for electric insulation,the content of the component (A) is preferably in the range from 0.1 to5 weight %, more preferably in the range from 0.5 to 3 weight %.

The component (B) comprises many kinds of reactive unsaturated monomershaving the structure of general formula [2]: ##STR10## wherein Y is anorganic group having a radical polymerizable unsaturated bond and R³, R⁴and R⁵ are an aryl, alkyl or substituted alkyl group, respectively, andmay be the same or different with each other.

Preferable compounds as the unsaturated monomer of the component (B) area reactive unsaturated monomer (b₁) having the structure of generalformula [5] and a reactive unsaturated monomer (b₂) having the structureof general formula [6]. The reactive unsaturated monomer (b₁) havingstructure of general formula [5] is more preferable among thesecompounds. ##STR11## In the formula [5], R¹³ is a hydrogen atom ormethyl group. In both of the formula [5] and the formula [6], Ph Isphenylene group and R¹⁴, R¹⁵ and R¹⁶ are an aryl, alkyl, substitutedalkyl or hydroxyl group, respectively. Preferably, the alkyl group andthe substituted alkyl group have 1 to 6 carbon atoms. More preferably,at least one of R¹⁴, R¹⁵ and R¹⁶ is hydroxyl group. The reactiveunsaturated monomer (b₁) and the reactive unsaturated monomer (b₂) maybe utilized as a salt, such as salt of hydrochloric acid, forcopolymeration with a (meth)acrylic ester monomer to adjust reactivityin the copolymerization.

Examples of the reactive unsaturated monomer (b₁) are:1,1-dimethyl-1-(2-hydroxypropyl)aminemethacrylimide,1,1-dipropyl-1-(2-hydroxypropyl)aminemethacrylimide, 1,1-dimethyl-1-(2,3-dihydroxypropyl)aminemethacylimide,1,1-dimethyl-1-(2,3-dihydroxypropyl) aminemethacrylimide,1,1-dipropyl-1-(2-hydroxy-butyl)amineacrylimide, 1,1-dimethyl-1-(2-hydroxyoctyl)aminemethacrylimide,1,1-dimethyl-1-(2-hydroxy-3-phenoxypropyl)-aminemethacrylimide,1,1-dimethyl- 1-(2-hydroxy-3-methoxy-propyl)aminemethacylimide, and1,1-dimethyl- 1-(2-hydroxy-2phenylethyl)aminemethacrylimide. Preferableexamples among these example are 1,1-dimethyl-1-(2-hydroxypropyl)amine-methacrylimide and1,1-dimethyl-1-(2,3-dihydroxproyl)amine-methacrylimide.

Examples of the reactive unsaturated monomer (b₂) are:1,1-dimethyl-1-(2- hydroxypropyl)amine 4-isopropenylbenzimide and1,1-dimethyl-1-(2-hydroxy-3-phenoxypropyl)amine 4-vinylbenzimide. Thepreferable example is 1,1-dimethyl- 1-(2-hydroxypropyl)amine4-isopropenylbenzimide.

The unsaturated monomer of the component (B) may be utilized singly oras the combination of two or more kinds thereof in the component (B).

The unsaturated monomer of the component (B) functions as a crosslinkingcomponent and provides the acrylic copolymer having large rate ofcrosslinking, small increase of adhesive strength and good removability.It functions more effectively in cooperation with the unsaturatedmonomer of the component (A).

When an isocyanate compound or an epoxy compound is used as an externalcrosslinking agent, the unsaturated monomer of the component (B) isadvantageously utilized because the function of the component (B)is-promoted by catalytic effect of the component (A).

The content of the component (B) is generally in the range from 0.01 to10 weight %. When the content of the component (B) is less than 0.01weight %, blisters are formed and removability is poor because ofinsufficient cohesive strength. When the content of the component (B) ismore than 10 weight %, the adhesive strength is remarkably decreasedbecause of too high cohesive strength.

The preferable content of the component (B) is different according tothe application to which the pressure sensitive adhesive of theinvention is utilized. When it is utilized as the blister resistantpressure sensitive adhesive, the content of the component (B) ispreferably in the range from 0.05 to 5 weight %, more preferably in therange from 0.2 to 3 weight %. When it is utilized as the P.S.A. forsurface protection, the content of the component (B) is preferably inthe range from 0.5 to 8 weight %, more preferably in the range from 0.5to 5 weight %. When it is utilized as the P.S.A. for electricinsulation, the content of the component (B) is preferably in the rangefrom 0.5 to 3 weight %, more preferably in the range from 1 to 2 weight%.

The unsaturated monomer of the component (C) is an unsaturated monomerhaving the structure of general formula [3]: ##STR12## wherein R⁶, R⁷,R⁸, R⁹ and R¹⁰ are a hydrogen atom or --CH₂ OH group, respectively, andmay be the same or different with each other. Examples of theunsaturated monomer of the component (C) are diacetoneacrylamide,hydroxymethyldiacetoneacrylamide and the like. Preferable example isdiacetoneacrylamtde.

The unsaturated monomer of the component (C) may be utilized singly oras the combination of two or more kinds thereof in the component (C).

When the unsaturated monomer of the component (C) is comprised in theacrylic copolymer, the copolymer has a property to absorb gas generatedin the composition. In the cases where plastic film or the like used asthe substrate sheet of the adhesive sheet works as a barrier layer for asmall mount of gas generated in the adhesive layer, the component (C)functions effectively to prevent formation of blisters which are to beformed as bubbles of the enclosed gas.

The content of the component (C) is generally in the range from 0 to 10weight %, preferably in the rage from 0.01 to 10 weight % and morepreferably in the range from 1 to 5 weight %. When the content of thecomponent (C) is more than 10 weight %, the adhesive strength isdecreased because of too high cohesive strength.

The unsaturated monomer of the component (D) is an unsaturated monomerhaving the structure of general formula [4]: ##STR13## wherein R¹¹ is ahydrogen atom or methyl group and R¹² is an alkyl group of 1 to 14carbon atoms, preferably 1 to 8 carbon atoms.

The component (D) is utilized in the acrylic copolymer to provide theadhesive composition with excellent weatherability, heat resistance anddurability.

Examples of the unsaturated monomer of the component (D) are methylacrylate, ethyl acrylate, butyl acrylate, decyl acrylate, 2-ethylhexylacrylate, isooctyl acrylate and the like and corresponding esters ofmethacrylic acid. Preferable examples of the unsaturated monomer aremethyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexylacrylate.

The unsaturated monomer of the component (D) may be utilized singly oras the combination of two or more kinds thereof in the component (D).When a combination of two or more kinds is utilized, the combination ofmethyl acrylate and 2-ethylhexyl acrylate and the combination of ethylacrylate and butyl acrylate are preferable. When the combination ofmethyl acrylate and 2-ethylhexyl acrylate is utilized, the content ofmethyl acrylate is generally in the range from 20 to 50 weight % and thecontent of 2-ethylhexyl acrylate is generally in the range from 50 to 80weight %. When the combination of ethyl acrylate and butyl acrylate isutilized, the content of ethyl acrylate is generally in the range from 5to 50 weight % and the content of butyl acrylate is generally in therange from 50 to 95 weight %.

The content of the component (D) in the acrylic copolymer is generallyin the range from 60 to 99.89 weight %, preferably in the range from 67to 99.84 weight % and more preferably in the range from 80 to 98.3weight %.

In the pressure sensitive adhesive composition of the invention, 50weight % or less of the component (D) of the acrylic copolymer may bereplaced by a copolymerizable unsaturated monomer other than thecomponent (D) which is copolymerizable with the unsaturated monomers ofeach of the component (A), the component (B), the component (C) and thecomponent (D).

The examples of the copolymerizable unsaturated monomer other than thecomponent (D) are vinyl esters, such as vinyl formate, vinyl acetate andthe like; acrylonitriles, such as acrylonitrile and the like; acrylates,such as dialkylaminoalkylene acrylate, glycidyl acrylate, hydroxyethylacrylate, hydroxypropyl acrylate and the like; methacrylates, such asdialkylaminoalkylene methacrylate, glycidyl methacrylate, hydroxyethylmethacrylate, acetoacetoxyethyl methacrylate and the like; acrylamides,such as acrylamide, N-n-butoxymethylacrylamide, N-methylolacrylamide andthe like; acrylic acid isocyanates, such as acrylic acid ethylisocyanate and the like; vinylsfianes, such as alkoxyvinylsfiane and thelike; and acrylic acids, such as acrylic acid, methacrylic acid,itaconic acid, maleic anhydride and the like. Preferable examples amongthese compounds are vinyl acetate, glycidyl acrylate, glycidylmethacrylate, hydroxyethyl acrylate and hydroxyethyl methacrylate.

The kind of the copolymerizable unsaturated monomer other than thecomponent (D) and the mount thereof utilized in the acrylic copolymer isselected according to the purpose of application of the pressuresensitive adhesive composition prepared by utilizing the acryliccopolymer. When more than 50% of the component (D) is replaced by thecopolymerizable unsaturated monomer, the pressure sensitive adhesivecomposition prepared becomes too hard and is not suitable as theadhesive composition to achieve the object of the invention.

The acrylic copolymer can be prepared by copolymerizing the component(A), the component (B), the component (C), the component (D) and theoptionally utilized copolymerizable unsaturated monomer by variousconventional methods of copolymerization. Examples of the conventionalmethods of copolymerization are solution copolymerization in a solvent,such as toluene, hexane, ethyl acetate and the like; emulsioncopolymerization in water; and bulk copolymerization substantially inthe absence of any organic solvents to prepare a low molecular weightcopolymer which is suitable for coating. For the purpose of improvingweatherability, heat resistance and solvent resistance, crosslinkingagents may be added to the composition in a suitable amount, ifnecessary, by diluting with a solvent.

The acrylic copolymer of the invention prepared by the method describedabove gives the pressure sensitive adhesive composition having excellentblister resistance, removability without staining and no corrosiveproperty against metals. To prepare the adhesive composition havingimproved weatherability, heat resistance and solvent resistance, acrosslinking agent may be added to the composition in an amount of from0.01 to 10 weight parts based on 100 weight parts of the basecomposition.

The kind of the crosslinking agent is not particularly limited.Preferable examples of the crosslinking agent are polyfunctionalisocyanate compounds, polyfunctional epoxy compounds, metal chelatecompounds and the like. The kind of the crosslinking agent and the mountthereof utilized in the adhesive composition is determined according tothe kinds of the unsaturated monomers utilized in the acrylic copolymerand the purpose of application of the pressure sensitive adhesivecomposition prepared by utilizing the acrylic copolymer.

Agents generally utilized in conventional pressure sensitive adhesivematerials, such as antioxadants, ultraviolet absorbing agents,tackifiers like rosin, phenolic resins, petroleum resins and the like,and like other agents, may be added to the adhesive compositionaccording to necessity.

The pressure sensitive adhesive composition of the invention may beutilized as the pressure sensitive adhesive material by directapplication or as a coated composit on a substrate, such as a plate, afilm, a sheet, paper and the like, or on a label substrate.

Thickness of the layer of the pressure sensitive adhesive composition ofthe invention coated on a substrate, such as a sheet, or on a labelsubstrate is not particularly limited. The thickness is generally in therange from 1 to 100 μm and preferably in the range from 5 to 30 μm.

It is preferable that the surface of the substrate, such as a sheet, isprocessed with a surface treatment, such as corona discharge treatment,plasma treatment and coating of primer, to provide better adhesivenesswith the pressure sensitive adhesive composition.

Sheets or plastic molded articles may be formed into a laminated productby utilizing the pressure sensitive adhesive composition of theinvention as the adhesive layer in the laminate.

Thickness of the adhesive layer in the laminate is not particularlylimited but suitably selected according to the requirement ofapplication. The thickness is generally in the range from 1 to 100 μmand preferably in the range from 5 to 30 μm.

Examples of the sheets utilized in the invention are plates, films,sheets and the like. Plastic sheets are preferably utilized and plasticsheets having transparency are more preferably utilized.

Material of the plastic sheets are not particularly limited but variouskinds of plastics can be utilized. Examples of the plastics arepolyolefin resins, such as polyethylene, polypropylene and the like;polyolefins containing chlorine, such as polyvinyl chloride and thelike; aromatic vinyl resins, such as polystyrene and the like; acrylicresins, such as polymethyl methacrylate and the like; polycarbonateresins; polyester resins, such as polyethylene terephthalate and thelike; polyallylate resins; polyether resins; and the like otherplastics. Preferable example of the plastics is polyethyleneterephthalate.

The plastic sheets may have a single layer structure or a multi-layerstructure. The plastic sheets may be treated with vapor deposition ofmetals, such as aluminum, copper and the like, surface coating withdyestuffs or coloring.

Thickness of the sheet utilized in the invention is not particularlylimited but suitably selected according to the requirement ofapplication. The thickness is generally in the range from 5 to 250 μmand preferably in the range from 15 to 80 μm.

Examples of the plastic molded articles utilized in the invention aremolded articles of various kinds of shape, such as films, sheets,plates, packaging containers, bottles, bags and the like others.

Materials of the plastic molded articles are not particularly limitedbut may be various kinds of plastics. Gas generating plastics whichgenerate small amounts of gas during a long period of time arepreferable materials for the pressure sensitive adhesive composition ofthe invention when the object of the invention is referred.

Many kinds of the gas generating resins are known. Examples of resinswhich generate rather remarkable amount of gas are resins comprising 5mol % or more, particularly 15 mol % or more, of aromatic ring, such aspolystyrene resins and polycarbonate resins, acrylic resins, such aspolymethyl methacrylate and the like and polyolefm resins, such aspolyethylene immediately after molding.

The polystyrene resins described above are resins which utilize 10weight % or more, particularly 30 weight % or more, of styrene monomerin the process of preparation of the resin, such as polystyrene resins,high impact resistance polystyrene resins,acrylonitrile-butadiene-styrene resins, acrylonitrile-styrene resins,methyl methacrylate-butadiene-sytrene resins, acrylicrubber-acrylonitrile-styrene resins, acrylonitrile-(ethylene propylenerubber)-styrene resins, acrylonitrile-(chlorinated polyethylene)styreneresins, noryl resins and the like resins. These resins are considered togenerate gaseous styrene monomer after molding to cause the formation ofblisters.

The resins comprising 5 mol % or more, particularly 15 mol % or more, ofaromatic rings have tendency to absorb moisture or to adsorb lowmolecular weight substances even if they do not comprise monomeric unitsof styrene and blisters are formed by generation of gas from theabsorbed moisture or adsorbed low molecular weight substances. The samekind of phenomenon takes place in case of the polymers having polargroups in the side group, such as acrylic resins.

Polyolefins, such as polyethylene, do not usually generate small amountsof gas continuously. However, these resins generate gas immediatelyafter molding to cause the formation of blisters. Preparation oflaminates with the adhesive layer formed by utilizing the pressuresensitive adhesive composition of the invention is effective forpreventing such an undesirable phenomenon.

Examples of the plastic molded articles utilized favorably in theinvention are polycarbonate resin plates for window panes, polymethylmethacrylate resin plates for window panes and molded articles ofpolystyrene, such as cassette tape cases made of polystyrene resins ofgood transparency. When pressure sensitive sheets are applied to thesurface of polycarbonate resin plates for window panes or polymethylmethacrylate resin plates for window panes for the purpose of adjustmentof sun light transmission or protection of the surface from scratching,blisters are particularly remarkable when they are formed. When pressuresensitive adhesive labels are applied to the surface of polystyrenemolded articles of good transparency, blisters are also particularlyremarkable when they are formed. Formation of blisters is actually aserious problem on polystyrene cases used as containers of magnetictapes.

Lamination of sheets to such kinds of plastic molded articles through anadhesive layer utilizing the pressure sensitive adhesive composition ofthe invention is the remarkably effective method of preventing theseproblems.

The plastic molded articles described above comprise articles having theplastic layers at the surface of the article made of other materials aswell as articles wholly made of the plastics.

The laminated products of the invention can be prepared by variousmethods. For example, the pressure sensitive adhesive composition iscoated on the surface of sheets and the coated sheets are applied to thesurface of plastic molded articles. As another example, the pressuresensitive adhesive composition is coated on the surface of moldedplastic articles and sheets are applied to the surface of the moldedplastic articles coated with the adhesive composition.

It is preferable that the surface of the plastic molded articles isprocessed with a surface treatment, such as corona discharge treatment,plasma treatment, coating of a primer and the like treatments, toprovide better adhesive property with the adhesive composition beforeapplication of the adhesive composition.

The laminated products of the invention can be utilized in many kinds ofapplication. Preferable examples of the application are window panes andcases for cassette tapes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be understood more readily with reference to thefollowing examples; however these examples are intended to illustratethe invention and are not to be construed to limit the scope of theinvention.

EXAMPLE 1

    ______________________________________                                        Butyl acrylate         60    weight parts                                     Ethyl acrylate         40    weight parts                                     N,N-dimethylaminopropylacrylamide                                                                    3     weight parts                                     The unsaturated monomer                                                                              1     weight parts                                     having the following formula:                                                  ##STR14##                                                                    2,2'-azo-bis-isobutyronitrile                                                                        0.5   weight parts                                     ______________________________________                                    

The components shown above were dissolved into a mixture of 90 weightparts of ethyl acetate and 20 weight parts of n-hexane and the solutionwas stirred at 70° C. for 12 hours for polymerization. To the viscoussolution thus prepared, 50 weight parts of toluene was added to dilutethe solution and a solution of acrylic copolymer was prepared.Conversion of the polymerization was 98%, viscosity was 25,000 cps andcontent of the solid component was 38.5%.

EXAMPLE 2

To 100 weight parts of the solution of acrylic copolymer prepared inExample 1, 2 weight parts of Coronate L® (a product of NipponPolyurethane Co., Ltd., a polyfunctional isocyanate compound) was addedand mixed. Thus, a pressure sensitive adhesive composition was prepared.

EXAMPLE 3

To 100 weight parts of the solution of acrylic copolymer prepared inExample 1, 0.25 weight parts of Adeka Resin EP-4100E® (a product ofAsahi Denka Co., Ltd., a polyfunctional epoxy compound) was added andmixed. Thus, a pressure sensitive adhesive composition was prepared.

EXAMPLE 4

    ______________________________________                                        2-Ethylhexyl acrylate                                                                             60      weight parts                                      Methyl acrylate     30      weight parts                                      Vinyl acetate       10      weight parts                                      N,N-dimethylaminopropyl-                                                                          3       weight parts                                      methacrylamide                                                                The unsaturated monomer                                                                           1.2     weight parts                                      having the following formula:                                                  ##STR15##                                                                    2,2'-azo-bis-isobutyronitrile                                                                     0.5     weight parts                                      ______________________________________                                    

The components shown above were dissolved into a mixture of 90 weightparts of ethyl acetate and 20 weight parts of n-hexane and a solution ofacrylic copolymer was prepared by the same method as in Example 1.Conversion of the polymerization was 97 %, viscosity was 9,300 cps andcontent of the solid component was 38.2%. To 100 weight parts of thesolution of acrylic copolymer prepared here, 0.25 weight parts of AdekaResin EP-4100E® (a product of Asahi Denka Co., Ltd., a polyfunctionalepoxy compound) was added and mixed. Thus, a pressure sensitive adhesivecomposition was prepared.

EXAMPLE 5

    ______________________________________                                        Butyl acrylate         60     weight parts                                    Ethyl acrylate         40     weight parts                                    N,N-dimethylaminopropylacrylate                                                                      3      weight parts                                    The unsaturated monomer                                                                              1      weight parts                                    having the following formula:                                                  ##STR16##                                                                    The unsaturated monomer                                                                              3      weight parts                                    having the following formula:                                                  ##STR17##                                                                    2,2'-azo-bis-isobutyronitrile                                                                        0.3    weight parts                                    ______________________________________                                    

The components shown above were dissolved into a mixture of 90 weightparts of ethyl acetate and 20 weight parts of n-hexane and a solution ofacrylic copolymer was prepared by the same method as in Example 1.Conversion of the polymerization was 98.2%, viscosity was 21,000 cps andcontent of the solid component was 39.3%. To 100 weight parts of thesolution of acrylic copolymer prepared here, 0.25 weight parts of AdekaResin EP-4100E® (a product of Asahi Denka Co., Ltd., a polyfunctionalepoxy compound) was added and mixed. Thus, a pressure sensitive adhesivecomposition was prepared.

Comparative Example 1

By using 60 weight parts of butyl acrylate, 40 weight parts of ethylacrylate and 3 weight parts of acrylic acid, a solution of acryliccopolymer was prepared by the same method as in Example 1.

A pressure sensitive adhesive composition was prepared by adding andmixing 2 weight parts of Coronate L® to 100 weight parts of the solutionof acrylic copolymer prepared here.

Comparative Example 2

A pressure sensitive adhesive composition was prepared by the samemethod as in Comparative example 1 except that 0.25 weight parts ofAdeka Resin EP-4 100E® was used in place of Coronate L®.

Comparative Example 3

A solution of acrylic copolymer was prepared by the same method as inExample 1 except that N,N-dimethylaminopropylacrylamide was not used. Apressure sensitive adhesive composition was prepared by adding andmixing 0.25 weight parts of Adeka Resin EP-4100E® to 100 weight parts ofthe solution of acrylic copolymer prepared here.

Comparative Example 4

A solution of acrylic copolymer was prepared by the same method as inExample 1 except that the unsaturated monomer having the formula:##STR18## was not used. A pressure sensitive adhesive composition wasprepared by adding and mixing 0.25 weight parts of Adeka Resin EP-4100E®to 100 weight parts of the solution of acrylic copolymer prepared here.

The solution of a pressure sensitive adhesive composition prepared in anExample or a Comparative example was coated on the surface of polyesterfilm of 25 μm thickness so that the coating layer has 20±2 g/m² of theadhesive composition and the thickness of 18 μm. The coated film wasdried by hot air stream at 100° C. for 1 minute and a pressure sensitiveadhesive sheet was prepared.

The results of the evaluation of the pressure sensitive adhesive sheetsthus prepared are shown in Table 1.

The solution of a pressure sensitive adhesive composition prepared in anExample or a Comparative example was diluted with toluene to prepare asolution having the solid content of 20%. The diluted solution wasdirectly coated on the surface of a polyethylene film of 70 μm thicknesspretreated with corona discharge so that the coating layer has thicknessof 5 μm. The coated film was heated at 70° C. for 3 minutes and aged inan drying oven at 50° C. for 20 hours and a surface protecting sheet wasprepared.

The results of the evaluation of the surface protecting sheet thusprepared are shown in Table 2.

The results in Table 1 and Table 2 clearly show the advantage of thepressure sensitive adhesive compositions and the pressure sensitiveadhesive sheets of the invention.

The evaluation shown in Table 1 was conducted according to the followingmethods.

(1) Ball tack

Ball tack was measured according to J. Dow's method (Japanese IndustrialStandard Z-0237), and shown by the stopped ball number.

(2) Adhesive strength

Adhesive strength when the sample was peeled at 180° angle was measuredaccording to the method of Japanese Industrial Standard Z-0237 and shownby the value of force in gram per 25 mm width. The measurement was made20 minutes after the sample was applied to the test substrate.

(3) Holding power

Holding power was measured at 40° C. under the loading of 1 kg accordingto Japanese Standard Z-0237 and shown by the time before dropping insecond. The measurement was stopped at the time of 18,000 seconds. Whenthe evaluation is shown as NC, no displacement of the sample wasobserved.

(4) Resistance against formation of blisters

A pressure sensitive adhesive sheet was applied to a transparentpolycarbonate plate (a product of Nippon Test Panel Co., Ltd., havingthickness of 2 mm) or a transparent acrylic plate (a product of NipponTest Panel Co., Ltd., having thickness of 2 mm). After the plate withthe pressure sensitive adhesive sheet was left standing for 1 hour in anair conditioned room adjusted to 23° C. and 65% relative humidity, itwas heated for acceleration by standing for 1 hour in a heated airdrying oven at 80° C. and the formation of blisters was evaluated byvisual observation. The result of the evaluation is expressed by thefollowing notations:

excellent: no formation of blisters was found.

good: small bubbles were found by a magnifying glass (10 times) in smallnumbers but no lifting was found.

fair: partial bubbles and liftings were found.

poor: bubbles and liftings were found all over.

(5) Corrosion resistance

A pressure sensitive adhesive sheet was applied to a copper plate (aproduct of Nippon Test Panel Co., Ltd.). After the plate with thepressure sensitive adhesive sheet was left standing in an airconditioned vessel adjusted to 50° C. and 90% relative humidity for 1day, the adhesive sheet was removed from the copper plate and formationof rust was evaluated by visual observation. The result of theobservation is expressed by the following notations:

good: no formation of rust was observed.

fair: slight formation of rust was observed.

poor: rust is formed and the surface turned black.

The evaluation shown in Table 2 was conducted according to the followingmethods.

(1) Initial adhesive strength

A pressure sensitive adhesive sheet for surface protection was appliedto a stainless steel plate (SUS #304) which had been polished with Emerypaper #280. Adhesive strength when the sample was peeled at 180° anglewas measured 20 minutes after the sample was applied to the testsubstrate and shown by the value of force in gram per 25 mm width.

(2) Adhesive strength

A pressure sensitive adhesive sheet for surface protection having thesize of 20×150 mm was applied to a stainless steel plate (SUS #304)which had been polished with Emery paper #280 and irradiated from theback side by using a weathermeter manufactured by Toyo Rika Kogyo Co.,Ltd. for a specified period of time. Adhesive strength of the pressuresensitive adhesive sheet to the stainless steel plate was measured bythe method of 180° peeling after the irradiation.

(3) Removability

The adhesive sheet for surface protection in a sample which was preparedand irradiated by using a weathermeter by the same method as in theevaluation of adhesive strength was removed vigorously from thestainless steel plate and the removability of the adhesive sheet fromthe stainless plate was evaluated by visual observation. The result ofthe observation is expressed by the following notations:

good: removed smoothly without remaining adhesive layer.

fair: adhesive strength is high and the adhesive layer is fractured bycohesive fracture; a small amount of adhesive layer remained on thesurface of the stainless steel plate.

poor: adhesive strength is too high and the adhesive layer is fracturedtotally by cohesive fracture; a considerable amount of adhesive layerremained on the surface of the stainless steel plate.

(4) Staining

The adhesive sheet for surface protection in a sample which was preparedand irradiated by using a weathermeter by the same method as in theevaluation of adhesive strength was removed vigorously from thestainless steel plate and the staining of the surface of the stainlesssteel plate by the adhesive sheet was evaluated by visual observation.The result of the observation is expressed by the following notations:

good: no staining was found.

fair: a slight degree of cloudy staining was found.

poor: remaining of the adhesive layer was found on the surface of thestainless steel plate and staining of the surface of the stainless steelplate was observed.

While the invention has beer-particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details can be made therein without departing from the spirit andscope of the invention.

To summarize the advantages obtained by the invention, because thepressure sensitive adhesive composition of the invention comprises thespecific acrylic copolymer as the main component thereof, the formationof blisters, such as bubbles and liftings, is prevented when theadhesive composition is utilized for lamination of plastic moldedarticles, particularly molded articles of polycarbonate resins andmolded articles of acrylic resins. It is favorably utilized for pressuresensitive adhesive sheets for surface protection because increase ofadhesive strength is small, staining of the surface of the substrate isprevented and removability is excellent. It is also favorably utilizedfor electric insulation tapes because corrosion resistance, creepproperty and solvent resistance are excellent.

                                      TABLE 1                                     __________________________________________________________________________           Characteristics of the pressure sensitive adhesive sheet                           adhesive strength      resistance against formation                           (g/25 cm)              of blisters                                            polycarbonate                                                                         acrylic resin                                                                        holding power                                                                         polycarbonate                                                                         acrylic resin                                                                        corrosion                   Example                                                                              ball tack                                                                          plate   plate  (sec)   plate   plate  resistance                  __________________________________________________________________________    Example 1                                                                            11   1200    1500    3000   good    excellent                                                                            good                        Example 2                                                                             9   920     990    NC/18000                                                                              excellent                                                                             excellent                                                                            good                        Example 3                                                                            11   650     710    NC/18000                                                                              excellent                                                                             excellent                                                                            good                        Example 4                                                                            10   520     550    NC/18000                                                                              excellent                                                                             excellent                                                                            good                        Example 5                                                                            10   390     430    NC/18000                                                                              excellent                                                                             excellent                                                                            good                        Comparative                                                                           6   950     1200   10200   poor    poor   poor                        example 1                                                                     Comparative                                                                           7   1180    1200    2000   poor    poor   poor                        example 2                                                                     Comparative                                                                          11   440     500    15000   fair    good   good                        example 3                                                                     Comparative                                                                          11   590     580    11000   fair    good   fair                        example 4                                                                     __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        irradiation time of                                                           weathermeter (hour)                                                                         0       80     160   180   200                                  ______________________________________                                        Example 2                                                                     initial adhesive strength                                                                   290     --     --    --    --                                   adhesive strength                                                                           --      420    530   720   850                                  removability  --      good   good  good  good                                 staining      --      good   good  good  fair                                 Example 3                                                                     initial adhesive strength                                                                   210     --     --    --    --                                   adhesive strength                                                                           --      350    390   400   450                                  removability  --      good   good  good  good                                 staining      --      good   good  good  good                                 Example 4                                                                     initial adhesive strength                                                                   180     --     --    --    --                                   adhesive strength                                                                           --      250    290   490   550                                  removability  --      good   good  good  good                                 staining      --      good   good  fair  fair                                 Example 5                                                                     initial adhesive strength                                                                   150     --     --    --    --                                   adhesive strength                                                                           --      220    200   350   390                                  removability  --      good   good  fair  fair                                 staining      --      good   good  fair  fair                                 Comparative                                                                   example 1                                                                     initial adhesive strength                                                                   410     --     --    --    --                                   adhesive strength                                                                           --      550    820   1100  1300                                 removability  --      fair   fair  poor  poor                                 staining      --      fair   poor  poor  poor                                 Comparative                                                                   example 2                                                                     initial adhesive strength                                                                   390     --     --    --    --                                   adhesive strength                                                                           --      510    620   920   1300                                 removability  --      fair   fair  poor  poor                                 staining      --      good   fair  poor  poor                                 Comparative                                                                   example 3                                                                     initial adhesive strength                                                                   340     --     --    --    --                                   adhesive strength                                                                           --      410    490   720   800                                  removability  --      fair   fair  fair  poor                                 staining      --      good   fair  fair  poor                                 Comparative                                                                   example 4                                                                     initial adhesive strength                                                                   380     --     --    --    --                                   adhesive strength                                                                           --      450    510   690   780                                  removability  --      good   good  fair  poor                                 staining      --      fair   fair  poor  poor                                 ______________________________________                                    

What is claimed is:
 1. A pressure sensitive adhesive sheet comprising anadhesive coated substrate, said substrate being selected from the groupconsisting of paper and a synthetic resin film, said adhesive coatingcomprising a pressure sensitive adhesive composition which comprises anacrylic copolymer prepared by copolymerization of from 0.1 to 20 weight% of a component (A) comprising at least one unsaturated monomerselected from the group consisting of unsaturated monomers having thestructure of the formula: ##STR19## wherein R is a hydrogen atom ormethyl group, R¹ and R² are a hydrogen atom or an alkyl group of 1 to 4carbon atoms, respectively, n is an integer from 1 to 4 and R¹ and R²are the same or different;from 0.01 to 10 weight % of a component (B)comprising at least one unsaturated monomer selected from the groupconsisting of unsaturated monomers having the structure of the formula:##STR20## wherein Y is an organic group having a radical polymerizableunsaturated bond and R³, R⁴ and R⁵ are an aryl or an unsubstituted orsubstituted alkyl group, respectively, and are the same or differentwith each other; from 0 to 10 weight % of a component (C) comprising atleast one unsaturated monomer selected from the group consisting ofunsaturated monomers having the structure of the formula: ##STR21##wherein R⁶, R⁷, R⁸, R⁹ and R¹⁰ are a hydrogen atom or --CH₂ OH group,respectively, and are the same or different with each other; and from 60to 99.89 weight % of a component (D) comprising at least one unsaturatedmonomer selected from the group consisting of unsaturated monomershaving the structure of the formula: ##STR22## wherein R¹¹ is a hydrogenatom or methyl group and R¹² is an alkyl group of 1 to 14 carbon atoms.2. A pressure sensitive sheet as claimed in claim 1 wherein thecomposition contains from 0.01 to 10 weight parts of a crosslinkingagent per 100 weight parts of the acrylic copolymer.
 3. A pressuresensitive adhesive sheet as claimed in claim 1 wherein the component (A)is at least one monomer selected from the group consisting ofN,N-dimethylaminoethylacrylamide, N,N-dimethylaminoethylmethacrylamide,N,N-dimethylaminopropylacrylamide,N,N-dimethylaminopropylmethacrylamide, N,N-diethylaminoethylacrylamide,N,N-diethylaminoethylmethacrylamide, N,N-diethylaminopropylacrylamideand N,N-diethylaminopropylmethacrylamide; the component (B) is at leastone monomer selected from the group consisting of1,1-dimethyl-l-(2-hydroxypropyl)aminemethacrylimide,1,1-dimethyl-l-(2,3-dihydroxypropyl)aminemethacrylimide and1,1-dimethyl-l-(2-hydroxypropyl)amine 4-isopropenylbenzimide; thecomponent (C) is diacetoneacrylamide and/orhydroxymethyldiacetoneacrylamide; and the component (D) is at least onemonomer selected from the group consisting of methyl acrylate, ethylacrylate, butyl acrylate, decyl acrylate, 2-ethylhexyl acrylate,isooctyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, decyl methacrylate, 2-ethylhexyl methacrylate and isooctylmethacrylate.
 4. A pressure sensitive label comprising an adhesivecoated substrate, said substrate being selected from the groupconsisting of paper and a synthetic resin film, said adhesive coatingcomprising a pressure sensitive adhesive composition which comprises anacrylic copolymer prepared by copolymerization of from 0.1 to 20 weight% of a component (A) comprising at least one unsaturated monomerselected from the group consisting of unsaturated monomers having thestructure of the formula: ##STR23## wherein R is a hydrogen atom ormethyl group, R¹ and R² are a hydrogen atom or an alkyl group of 1 to 4carbon atoms, respectively, n is an integer from 1 to 4 and R¹ and R²are the same or different;from 0.01 to 10 weight % of a component (B)comprising at least one unsaturated monomer selected from the groupconsisting of unsaturated monomers having the structure of the formula:##STR24## wherein Y Is an organic group having a radical polymerizableunsaturated bond and R³, R⁴ and R⁵ are an aryl or an unsubstituted orsubstituted alkyl group, respectively, and are the same or differentwith each other. from 0 to 10 weight % of a component (C) comprising atleast one unsaturated monomer selected from the group consisting ofunsaturated monomers having the structure of the formula: ##STR25##wherein R⁶, R⁷, R⁸, R⁹ and R¹⁰ are a hydrogen atom or --CH₂ OH group,respectively, and are the same or different with each other; and from 60to 99.89 weight % of a component (D) comprising at least one unsaturatedmonomer selected from the group consisting of unsaturated monomershaving the structure of the formula: ##STR26## wherein R¹¹ is a hydrogenatom or methyl group and R¹² is an alkyl group of 1 to 14 carbon atoms.5. A pressure sensitive label as claimed in claim 4, wherein thecomponent (A) is at least one monomer selected from the group consistingof N,N-dimethylaminoethyl-acrylamide,N,N-dimethylaminoethylmethacrylamide, N,N-dimethylaminopropylacrylamide,N,N-dimethylaminopropylmethacrylamide, N,N-diethylaminoethylacrylamide,N,N-diethylaminoethylmethacrylamide, N,N-diethylaminopropylacrylamideand N,N-diethylaminopropylmethacrylamide; the component (B) is at leastone monomer selected from the group consisting of1,1-dimethyl-l-(2-hydroxypropyl)aminemethacrylimide,1,1-dimethyl-l-(2,3-dihydroxypropyl)aminemethacrylimide and1,1-dimethyl-l-(2-hydroxypropyl)amine 4-isopropenylbenzimide; thecomponent (C) is diacetoneacrylamide and/orhydroxymethyldiacetoneacrylamide; and the component (D) is at least onemonomer selected from the group consisting of methyl acrylate, ethylacrylate, butyl acrylate, decyl acrylate, 2-ethylhexyl acrylate,isooctyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, decyl methacrylate, 2-ethylhexyl methacrylate and isooctylmethacrylate.
 6. A laminate which is prepared by laminating sheets orplastic molded articles which are held together by means of an adhesivelayer of a pressure sensitive adhesive composition, said compositioncomprising an acrylic copolymer prepared by copolymerization of from 0.1to 20 weight % of a component (A) comprising at least one unsaturatedmonomer selected from the group consisting of unsaturated monomershaving the structure of the formula: ##STR27## wherein R is a hydrogenatom or methyl group R¹ and R² are a hydrogen atom or an alkyl group of1 to 4 carbon atoms, respectively, n is an integer from 1 to 4 and R¹and R² are the same or different;from 0.01 to 10 weight % of a component(B) comprising at least one unsaturated monomer selected from the groupconsisting of unsaturated monomers having the structure of the formula:##STR28## wherein Y is an organic group having a radical polymerizableunsaturated bond and R³, R⁴ and R⁵ are an aryl or an unsubstituted orsubstituted alkyl group, respectively, and are the same or differentwith each other. from 0 to 10 weight % of a component (C) comprising atleast one unsaturated monomer selected from the group consisting ofunsaturated monomers having the structure of the formula: ##STR29##wherein R⁶, R⁷, R⁸, R⁹ and R.sup. 10 are a hydrogen atom or --CH ₂ OHgroup, respectively, and are the same or different with each other; andfrom 60 to 99.89 weight % of a component (D) comprising at least oneunsaturated monomer selected from the group consisting unsaturatedmonomers having the structure of the formula: ##STR30## wherein R¹¹ is ahydrogen atom or methyl group and R¹² is an alkyl group of 1 to 14carbon atoms.
 7. A laminate as claimed in claim 6 wherein the component(A) is one or more kinds of unsaturated monomers selected from the groupconsisting of N,N-dimethylamlnoethylacrylarnlde,N,N-dlmethylamtnoethylmethacrylamide, N,N-dimethylaminopropylacrylamide,N,N-dimethylaminopropylmethacrylamide, N,N-diethylaminoethylacrylamide,N,N-diethylamlnoethylmethacrylamide, N,N-diethylaminopropylacrylamldeand N,N-diethylaminopropylmethacrylamide.
 8. A laminate as claimed inclaim 6 wherein the component (B) is one or more kinds of unsaturatedmonomers selected from the group consisting of1,1-dimethyl-1-(2-hydroxypropyl)aminemethacrylimide,1,1-dimethyl-1-(2,3-dihydroxypropyl)aminemethacrylimide and1,1-dimethyl- 1-(2-hydroxypropyl)amine 4-isopropenylbenzimide.
 9. Alaminate as claimed in claim 6 wherein the component (C) isdiacetoneacrylamide and/or hydroxymethyldiacetoneacrylamide.
 10. Alaminate as claimed in claim 6 wherein the component (D) is one or morekinds of unsaturated monomers selected from the group consisting ofmethyl acrylate, ethyl acrylate, butyl acrylate, decyl acrylate,2-ethylhexyl acrylate, isooctyl acrylate, methyl methacrylate ethylmethacrylate, butyl methacrylate, decyl methacrylate, 2-ethylhexylmethacrylate and isooctyl methacrylate.
 11. A laminate as claimed inclaim 6 wherein the component (D) is the combination of methyl acrylateand 2-ethylhexyl acrylate or the combination of ethyl acrylate and butylacrylate.
 12. A laminate as claimed in claim 6 wherein the content ofthe component (A) in the acrylic copolymer is in the range from 0.1 to15 weight %.
 13. A laminate as claimed in claim 1 wherein the content ofthe component (A) in the acrylic copolymer is in the range from 0.5 to10 weight %.
 14. A laminate as claimed in claim 1 wherein the content ofthe component (B) in the acrylic copolymer is in the range from 0.05 to8 weight %.
 15. A laminate as claimed in claim 1 wherein the content ofthe component (B) in the acrylic copolymer is in the range from 0.2 to 5weight %.
 16. A laminate as claimed in claim 1 wherein the content ofthe component (C) in the acrylic copolymer is in the range from 0.01 to10 weight %.
 17. A laminate as claimed in claim 1 wherein the content ofthe component (D) in the acrylic copolymer is in the range from 67 to99.84 weight %.
 18. A laminate as claimed in claim 1 wherein 50 weight %or less of the component (D) of the acrylic copolymer is replaced by acopolymerizable unsaturated monomer other than the component (D) whichis copolymerizable with the unsaturated monomers of each of thecomponent (A), the component (B), the component (C) and the component(D).
 19. A laminate as claimed in claim 6 wherein the pressure sensitiveadhesive composition contains a crosslinking agent in an mount in therange from 0.01 to 10 weight parts per 100 weight parts of the acryliccopolymer.
 20. A laminate as claimed in claim 6 wherein the plasticmolded article is a molded article of a polycarbonate resin, an acrylicresin or a polystyrene resin.
 21. A laminate as claimed in claim 6wherein the plastic molded article is selected from the group consistingof a polycarbonate resin plate for a window pane, a polymethylmethacrylate resin plate for a window pane and a transparent moldedarticle of a polystyrene resin.
 22. A laminate as claimed in claim 6,wherein the component (A) is at least one monomer selected from thegroup consisting of N,N-dimethylaminoethylacrylamide,N,N-dimethylaminoethylmethacrylamide, N,N-dimethylaminopropylacrylamide,N,N-dimethylaminopropylmethacrylamide, N,N-diethylaminoethylacrylamide,N,N-diethylaminoethylmethacrylamide, N,N-diethylaminopropylacrylamideand N,N-diethylaminopropylmethacrylamide; the component (B) is at leastone monomer selected from the group consisting of1,1-dimethyl-l-(2-hydroxypropyl)aminemethacrylimide,1,1-dimethyl-l-(2,3-dihydroxypropyl)aminemethacrylimide and1,1-dimethyl-l-(2-hydroxypropyl)amine 4-isopropenylbenzimide; thecomponent (C) is diacetoneacrylamide and/orhydroxymethyldiacetoneacrylamide; and the component (D) is at least onemonomer selected from the group consisting of methyl acrylate, ethylacrylate, butyl acrylate, decyl acrylate, 2-ethylhexyl acrylate,isooctyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, decyl methacrylate, 2-ethylhexyl methacrylate and isooctylmethacrylate.